A process for extracting potassium chloride from carnallite

Abstract

The application provides a method for extracting potassium chloride from carnallite, and belongs to the technical field of comprehensive utilization of salt lake resources. The method comprises the following steps: mixing the carnallite with a mixed salt solution (circulating mother liquor) and then performing salting-out crystallization conversion to obtain a reaction slurry; performing solid-liquid separation on the reaction slurry to obtain coarse potassium chloride solid and a magnesium-containing decomposition mother liquor; performing leaching on the coarse potassium chloride solid and then drying to obtain potassium chloride. The method is simple to operate, easy to industrialize, does not pollute the environment, realizes potassium-magnesium separation under normal temperature conditions, does not need the high-temperature evaporation process of the hot-solution crystallization method, does not need a flotation reagent, greatly reduces energy consumption and equipment corrosion problems, and is low in production cost. The application realizes the recycling of the magnesium-containing decomposition mother liquor and the leaching solution, reduces wastewater discharge, conforms to the concept of clean production and circular economy, and is environmentally friendly. The potassium chloride product obtained by the application is suitable in purity, and can be directly put into high-magnesium brine for a magnesium precipitation process, so as to promote magnesium salt crystallization and precipitation.

Description

Technical Field

[0001] This invention relates to the field of comprehensive utilization technology of salt lake resources, and in particular to a method for extracting potassium chloride from carnallite. Background Technology

[0002] Potassium chloride (potassium fertilizer) is an indispensable basic fertilizer in agricultural production. As the most important form of potassium resource occurrence in my country, the efficient development and utilization of carnallite deposits in salt lakes is of great practical significance for ensuring food security and self-sufficiency in potassium fertilizer supply. Currently, the industrial technology routes for extracting potassium from carnallite deposits are mainly divided into two categories: thermal crystallization and cold decomposition-flotation.

[0003] The thermal dissolution crystallization method utilizes the significant differences in the solubility of various components in carnallite at different temperatures to achieve potassium and magnesium separation through high-temperature dissolution and cooling crystallization. This method yields potassium chloride products with high purity and stable quality. However, the entire process requires operation under high-temperature conditions, resulting in enormous energy consumption. Furthermore, the high-temperature medium causes severe corrosion to the equipment, leading to high maintenance costs and large investment scale, making it difficult to promote large-scale economic application in my country's salt lake regions.

[0004] Cold decomposition-flotation is currently the most widely used potassium extraction process. Its core principle is to decompose carnallite with water at room temperature, so that magnesium chloride preferentially enters the liquid phase, potassium chloride crystallizes out, and then sodium chloride is separated by flotation. Compared with the hot dissolution method, the energy consumption of this process is significantly reduced, but due to its own technical characteristics, there are still the following insurmountable defects: (1) It is difficult to accurately control the amount of decomposition water. When the amount of water added is too low, magnesium chloride is not fully dissolved, and potassium chloride cannot be completely released from the carnallite lattice; when the amount of water added is too high, the precipitated potassium chloride is redissolved and lost, and a contradiction is formed between the decomposition rate and the recovery rate. (2) The overall potassium recovery rate is low. In the traditional process, the decomposition mother liquor rich in magnesium chloride is usually directly discharged or only simply treated and then discharged. A large amount of potassium resources entrained in the mother liquor cannot be effectively recovered, resulting in an overall recovery rate of less than 70% for the whole process, and serious waste of resources. In addition, the existing process does not recycle the rinsing liquid generated from washing crude potassium, in which the dissolved potassium is discharged, further reducing the overall recovery rate. (3) High dependence on flotation reagents. To achieve effective separation of potassium chloride and sodium chloride, various collectors, inhibitors and other chemical reagents need to be added, which not only increases the cost of raw materials, but also introduces organic pollutants, putting additional pressure on subsequent mother liquor treatment and environmental compliance. (4) Slime interferes with flotation effect. Fine slime impurities associated with carnallite ore are very easy to adhere to the mineral surface during flotation, interfering with the selective action of flotation reagents, resulting in a decrease in concentrate grade and fluctuations in flotation indicators. Although the cold decomposition-flotation method has formed a relatively mature process in production, the existing technical solutions generally treat magnesium-containing decomposition mother liquor and washing liquid as waste and discharge them into the system, failing to establish an effective liquid phase recycling mechanism. This process not only causes additional loss of potassium resources, but also increases water consumption and waste liquid discharge, which is incompatible with the development conditions of water scarcity and fragile ecological environment in the salt lake area.

[0005] In summary, existing processes still have significant shortcomings in terms of operational controllability, resource recovery rate, process economy, and environmental friendliness, particularly lacking methods for recycling magnesium-containing decomposition mother liquor and washing liquid. Therefore, this paper proposes a new method for potassium extraction from carnallite at room temperature, which requires no flotation reagents, achieves high potassium recovery, high water resource recycling rate, and is environmentally friendly. Summary of the Invention

[0006] The purpose of this invention is to provide a method for extracting potassium chloride from carnallite, in order to solve the problems of difficult precise control of decomposition water volume, low potassium recovery rate, high energy consumption, and unclear mother liquor recycling in the prior art.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for extracting potassium chloride from carnallite, comprising the following steps: 1) Carnallite is mixed with a mixed salt solution and then subjected to salting-out crystallization to obtain a reaction slurry; 2) The reaction slurry is subjected to solid-liquid separation to obtain crude potassium chloride solid and magnesium-containing decomposition mother liquor; 3) The crude potassium chloride solid was countercurrently leached with a circulating leaching solution. The leached solid was then dried to obtain potassium chloride.

[0008] Preferably, the magnesium-containing decomposition mother liquor in step 2) is mixed with water and returned to step 1) as a mixed salt solution for recycling, with the mass ratio of magnesium-containing decomposition mother liquor to water being 1~4:1; the rinsing liquid generated after countercurrent rinsing in step 3) is collected and not discharged externally, but returned to step 3) as the rinsing liquid for the next batch of crude potassium chloride solid. Steps 1) to 3) are repeated multiple times, with each cycle lasting 5 to 8 times.

[0009] Preferably, the carnallite is an ore obtained by sun-drying in potassium-containing brine or salt pans; the carnallite contains the following components by mass fraction: Li + 0.1~0.6%, Na + 0.1~0.5%, Ca 2+ 0.05~0.25%, K + 12.2~14.5%, Mg 2+ 8.5~10.4%, Cl - 45~52%, SO4 2- 0.5%~5%.

[0010] Preferably, the mixed salt solution is a circulating mother liquor, the solvent of the mixed salt solution is water, and the mixed salt contains one or more of potassium chloride, potassium sulfate, magnesium chloride, magnesium chloride hexahydrate, and magnesium sulfate.

[0011] Preferably, the liquid-to-solid ratio of the mixed salt solution to carnallite is 1.5~4 mL:1 g.

[0012] Preferably, the salting-out crystallization transformation temperature is 8~35℃, the salting-out crystallization transformation time is 0.5~2.5h, and the salting-out crystallization transformation is carried out under stirring conditions.

[0013] Preferably, the rinsing solution is one or more of potassium chloride, potassium sulfate, potassium nitrate and water, and the number of countercurrent rinsing cycles is ≥1.

[0014] Preferably, the liquid-to-solid ratio of the leaching solution to the crude potassium chloride solid is 0.2~3 mL:1 g.

[0015] The beneficial effects of this invention are: 1) This invention is based on K + Mg 2+ / / Cl- –H2O system phase diagram, by precisely controlling the composition and addition amount of mixed salt solution (circulating mother liquor), ensures that the liquid phase composition is in the optimal state during the decomposition process, magnesium chloride selectively dissolves while potassium chloride is supersaturated and precipitates, and with the recycling of mother liquor, the overall potassium recovery rate is significantly higher than that of traditional processes.

[0016] 2) This invention uses a magnesium-containing mixed salt solution (circulating mother liquor) as the decomposition medium. By controlling the amount of magnesium salt added, the amount of Mg in the liquid phase can be precisely adjusted. 2+ The concentration makes the decomposition process more controllable, and compared with the use of natural potassium-containing brine in existing technologies, it has the advantages of controllable composition and wide applicability.

[0017] 3) The method of the present invention is simple to operate, easy to industrialize, does not pollute the environment, and achieves potassium-magnesium separation at room temperature. It does not require the high-temperature evaporation process of hot melt crystallization method, nor does it require flotation reagents, which greatly reduces energy consumption and equipment corrosion problems, and has low production costs.

[0018] 4) This invention realizes the recycling of magnesium-containing decomposition mother liquor and rinsing liquid. The mother liquor is returned to the decomposition process after being replenished with water, and the rinsing liquid is recycled until saturation, which reduces wastewater discharge, conforms to the concept of clean production and circular economy, and is environmentally friendly.

[0019] 5) The potassium chloride product obtained by this invention has suitable purity and can be directly added to high magnesium brine for magnesium precipitation process to promote magnesium salt crystallization and realize the process of "potassium extraction from carnallite → magnesium precipitation with potassium chloride → lithium extraction from mother liquor" in salt lake resources. Detailed Implementation

[0020] This invention provides a method for extracting potassium chloride from carnallite, comprising the following steps: 1) Carnallite is mixed with a mixed salt solution and then subjected to salting-out crystallization to obtain a reaction slurry; 2) The reaction slurry is subjected to solid-liquid separation to obtain crude potassium chloride solid and magnesium-containing decomposition mother liquor; 3) The crude potassium chloride solid was countercurrently leached with a circulating leaching solution. The leached solid was then dried to obtain potassium chloride.

[0021] In this invention, the mass ratio of magnesium-containing decomposition mother liquor to water is preferably 2~3:1, and more preferably 2.6:1.

[0022] In this invention, the magnesium-containing decomposition mother liquor in step 2) is mixed with water and used as the mixed salt solution in step 1) and recycled back to step 1). The mass ratio of magnesium-containing decomposition mother liquor to water is 1~4:1. The rinsing liquid generated after countercurrent rinsing in step 3) is collected and not discharged externally, but returned to step 3) as the rinsing liquid for the next batch of crude potassium chloride solid. Steps 1) to 3) are repeated multiple times, preferably 5 to 8 times, and more preferably 6 to 7 times.

[0023] In this invention, the carnallite is preferably an ore obtained by sun-drying in potassium-containing brine or salt pans; the carnallite contains the following components by mass fraction: Li + 0.1~0.6%, preferably 0.2~0.5%, more preferably 0.3~0.4%; Na + 0.1~0.5%, preferably 0.2~0.4%, more preferably 0.3%; Ca 2+ 0.05~0.25%, preferably 0.1~0.2%, more preferably 0.15%; K + 12.2~14.5%, preferably 12.5~14%, more preferably 13~13.5%; Mg 2+ 8.5~10.4%, preferably 9~10%, more preferably 9.5%; Cl - 45-52%, preferably 47-50%, and even more preferably 48-49%; SO4 2- 0.5-5%, preferably 1-4%, and even more preferably 1.5-3%.

[0024] In this invention, carnallite also contains water of crystallization and trace impurities.

[0025] In this invention, the mixed salt solution is a circulating mother liquor, the solvent of the mixed salt solution is preferably water, and the mixed salt preferably contains one or more of potassium chloride, potassium sulfate, magnesium chloride, magnesium chloride hexahydrate and magnesium sulfate.

[0026] In this invention, the liquid-to-solid ratio of the mixed salt solution to carnallite is preferably 1.5-4 mL:1 g, more preferably 2-3.5 mL:1 g, and even more preferably 2.2-3 mL:1 g.

[0027] In this invention, the preferred temperature for the salting-out crystallization transformation is 8~35℃, more preferably 15~30℃, and even more preferably 23~25℃. The preferred time for the salting-out crystallization transformation is 0.5~2.5h, more preferably 0.8~1.6h, and even more preferably 1~1.5h. The salting-out crystallization transformation is preferably carried out under stirring conditions.

[0028] In this invention, the rinsing solution is preferably one or more of potassium chloride, potassium sulfate, potassium nitrate and water, and the number of countercurrent rinsings is ≥1.

[0029] In this invention, rinsing is used to remove impurities adhering to the surface of crude potassium chloride solid.

[0030] In this invention, the liquid-to-solid ratio of the rinsing solution to the crude potassium chloride solid is preferably 0.2-3 mL:1 g, more preferably 0.5-2.5 mL:1 g, and even more preferably 1-2 mL:1 g.

[0031] In this invention, the rinsing solution after rinsing is used as the rinsing solution for the next rinsing and is recycled until saturated.

[0032] This invention provides a novel room-temperature decomposition method for potassium extraction that is simple to operate, requires no flotation reagents, has a high potassium recovery rate, a high water resource recycling rate, and is environmentally friendly. By recycling the magnesium-containing decomposition mother liquor and leaching liquid, it provides a practical and feasible technical solution for the efficient and clean utilization of carnallite resources in salt lakes.

[0033] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0034] Example 1

[0035] (1) The main components of carnallite obtained from potassium-containing brine are: Li + 0.35%, Na + 0.3%, Ca 2+ 0.15%, K + 13.4%, Mg 2+ 9.5%, Cl - 48.5%, SO4 2- 2.0% of the final composition consisted of water of crystallization and trace impurities. A mixed salt solution (potassium chloride, magnesium chloride hexahydrate, and water in a mass ratio of 4.5:18.5:77.0) was added to carnallite. The liquid-to-solid ratio of the mixed salt solution to carnallite was 4 mL:1 g. The mixture was stirred at 400 rpm for 1.6 h at 15 °C to induce salt precipitation and crystallization. After the salt precipitation and crystallization were completed, solid-liquid separation was performed to obtain crude potassium chloride solid and magnesium-containing decomposition mother liquor. The grade of crude potassium chloride solid reached 85.9%. (2) Add water to the magnesium-containing decomposition mother liquor obtained by separation as a mixed salt solution for the next salting-out crystallization transformation, and return to step (1) for recycling. The mass ratio of magnesium-containing decomposition mother liquor to water is 2:1. (3) The crude potassium chloride solid was rinsed twice in countercurrent with a rinsing solution (the mass ratio of potassium chloride to water was 25:75). The liquid-solid ratio of the rinsing solution to the crude potassium chloride solid was 3 mL:1 g. The mother liquor and impurities attached to the surface were removed. After drying, the potassium chloride product was obtained with a grade of 92.6%. The rinsing solution was recycled for the next rinsing of the crude potassium chloride solid and was reused.

[0036] After eight cycles, the overall recovery rate of potassium chloride reached a stable level of 81.48%, with an overall grade of 92.31%.

[0037] Example 2

[0038] (1) The main components of carnallite obtained from potassium-containing brine are: Li + 0.6%, Na + 0.5%, Ca 2+ 0.25%, K + 14.5%, Mg 2+ 10.4%, Cl - 49%, SO4 2- The final composition was 3.0%, with the remainder being water of crystallization and trace impurities. A mixed salt solution (potassium chloride, magnesium chloride, and water in a mass ratio of 3:25:72) was added to carnallite, with a liquid-to-solid ratio of 1.5 mL to 1 g. The mixture was stirred at 400 rpm for 2.5 h at 8 °C to induce salt precipitation and crystallization. After the salt precipitation and crystallization were completed, solid-liquid separation was performed to obtain crude potassium chloride solid and magnesium-containing decomposition mother liquor. The grade of crude potassium chloride solid reached 84.6%. (2) Add water to the magnesium-containing decomposition mother liquor obtained by separation as a mixed salt solution for the next salting-out crystallization transformation, and return to step (1) for recycling. The mass ratio of magnesium-containing decomposition mother liquor to water is 1:1. (3) The crude potassium chloride solid was rinsed twice in a countercurrent manner with a rinsing solution (the mass ratio of potassium chloride, potassium sulfate and water was 24:3:73). The liquid-solid ratio of the rinsing solution to the crude potassium chloride solid was 2 mL:1 g. The mother liquor and impurities attached to the surface were removed. After drying, the potassium chloride product was obtained with a grade of 91.9%. The rinsing solution was recycled for the next rinsing of the crude potassium chloride solid and was reused.

[0039] After six cycles, the overall recovery rate of potassium chloride reached a stable level of 80.87%, with an overall grade of 91.58%.

[0040] Example 3

[0041] (1) The main component of carnallite obtained by sun-drying in salt fields is: Li + 0.38%, Na + 0.29%, Ca 2+ 0.16%, K + 12.8%, Mg 2+ 8.84%, Cl - 48.0%, SO4 2-The final composition consisted of 1.5% potassium chloride, with the remainder being water of crystallization and trace impurities. A mixed salt solution (potassium chloride, magnesium chloride hexahydrate, and water in a mass ratio of 5.5:15.5:79.0) was added to carnallite, with a liquid-to-solid ratio of 2.2 mL:1 g. The mixture was stirred at 400 rpm for 1 hour at 23°C to induce salt precipitation and crystallization. After the salt precipitation and crystallization were completed, solid-liquid separation was performed to obtain crude potassium chloride solid and magnesium-containing decomposition mother liquor. The grade of crude potassium chloride solid reached 89.4%. (2) Add water to the magnesium-containing decomposition mother liquor obtained by separation as a mixed salt solution for the next salting-out crystallization transformation, and return to step (1) for recycling. The mass ratio of magnesium-containing decomposition mother liquor to water is 2.6:1. (3) The crude potassium chloride solid was rinsed three times countercurrently with a rinsing solution (the mass ratio of potassium chloride to water was 26:74). The liquid-solid ratio of the rinsing solution to the crude potassium chloride solid was 1 mL:1 g. The mother liquor and impurities attached to the surface were removed. After drying, the potassium chloride product was obtained with a grade of 98.3%. The rinsing solution was recycled for the next rinsing of the crude potassium chloride solid and was reused.

[0042] After eight cycles, the overall recovery rate of potassium chloride reached a stable level of 82.37%, with an overall grade of 96.66%.

[0043] Example 4

[0044] (1) The main component of carnallite obtained by sun-drying in salt fields is: Li + 0.1%, Na + 0.1%, Ca 2+ 0.05%, K + 12.2%, Mg 2+ 8.5%, Cl - 47.0%, SO4 2- The final composition was 1.0%, with the remainder being water of crystallization and trace impurities. A mixed salt solution (the mass ratio of magnesium chloride hexahydrate to water was 22.0:78.0) was added to carnallite, with a liquid-to-solid ratio of 2.8 mL:1 g. The mixture was stirred at 400 rpm for 0.5 h at 35 °C to induce salt precipitation and crystallization. After the salt precipitation and crystallization were completed, solid-liquid separation was performed to obtain crude potassium chloride solid and magnesium-containing decomposition mother liquor. The grade of crude potassium chloride solid reached 84.3%. (2) Add water to the magnesium-containing decomposition mother liquor obtained by separation as a mixed salt solution for the next salting-out crystallization transformation, and return to step (1) for recycling. The mass ratio of magnesium-containing decomposition mother liquor to water is 4:1. (3) The crude potassium chloride solid was rinsed twice in a countercurrent manner with a rinsing solution (the mass ratio of potassium chloride, potassium sulfate and water was 22:2:76). The liquid-solid ratio of the rinsing solution to the crude potassium chloride solid was 0.2 mL:1 g. The mother liquor and impurities attached to the surface were removed. After drying, the potassium chloride product was obtained with a grade of 91.2%. The rinsing solution was recycled for the next rinsing of the crude potassium chloride solid and was reused.

[0045] After seven cycles, the overall recovery rate of potassium chloride reached a stable level of 80.54%, with an overall grade of 90.97%.

[0046] Example 5

[0047] (1) The main components of carnallite obtained from potassium-containing brine are: Li + 0.6%, Na + 0.1%, Ca 2+ 0.25%, K + 12.2%, Mg 2+ 9.8%, Cl - 50.0%, SO4 2- The final composition was 4.0%, with the remainder being water of crystallization and trace impurities. A mixed salt solution (potassium chloride, potassium sulfate, magnesium chloride, and water in a mass ratio of 4.0:2.5:20.0:73.5) was added to carnallite, with a liquid-to-solid ratio of 1.8 mL:1 g. The mixture was stirred at 400 rpm for 1.2 h at 28 °C for salting-out crystallization. After the salting-out crystallization was completed, solid-liquid separation was performed to obtain crude potassium chloride solid and magnesium-containing decomposition mother liquor. The grade of crude potassium chloride solid reached 87.9%. (2) Add water to the magnesium-containing decomposition mother liquor obtained by separation as a mixed salt solution for the next salting-out crystallization transformation, and return to step (1) for recycling. The mass ratio of magnesium-containing decomposition mother liquor to water is 3:1. (3) The crude potassium chloride solid was leached three times countercurrently with a leaching solution (the mass ratio of potassium chloride to water was 24.5:75.5). The liquid-solid ratio of the leaching solution to the crude potassium chloride solid was 0.6 mL:1 g. The mother liquor and impurities attached to the surface were removed. After drying, the potassium chloride product was obtained with a grade of 94.7%. The leaching solution was recycled for the next leaching of the crude potassium chloride solid and was reused.

[0048] After six cycles, the overall recovery rate of potassium chloride reached a stable level of 81.89%, with an overall grade of 94.05%.

[0049] Example 6

[0050] (1) The main components of carnallite obtained from potassium-containing brine are: Li + 0.45%, Na + 0.35%, Ca2+ 0.05%, K + 13.8%, Mg 2+ 10.4%, Cl - 49.0%, SO4 2- 2.5% of the final composition consisted of water of crystallization and trace impurities. A mixed salt solution (potassium chloride, magnesium chloride hexahydrate, and water in a mass ratio of 5.0:17.0:78.0) was added to carnallite, with a liquid-to-solid ratio of 2.5 mL:1 g. The mixture was stirred at 400 rpm for 0.9 h at 25 °C to induce salt precipitation and crystallization. After the salt precipitation and crystallization were completed, solid-liquid separation was performed to obtain crude potassium chloride solid and magnesium-containing decomposition mother liquor. The grade of crude potassium chloride solid reached 89.1%. (2) Add water to the magnesium-containing decomposition mother liquor obtained by separation as a mixed salt solution for the next salting-out crystallization transformation, and return to step (1) for recycling. The mass ratio of magnesium-containing decomposition mother liquor to water is 2.8:1. (3) The crude potassium chloride solid was rinsed twice in a countercurrent manner with a rinsing solution (the mass ratio of potassium chloride, potassium sulfate and water was 25:2:73). The liquid-solid ratio of the rinsing solution to the crude potassium chloride solid was 1.3 mL:1 g. The mother liquor and impurities attached to the surface were removed. After drying, the potassium chloride product was obtained with a grade of 96.3%. The rinsing solution was recycled for the next rinsing of the crude potassium chloride solid and was reused.

[0051] After seven cycles, the overall recovery rate of potassium chloride reached a stable level of 82.41%, with an overall grade of 95.58%.

[0052] Example 7

[0053] (1) The main component of carnallite obtained by sun-drying in salt fields is: Li + 0.25%, Na + 0.4%, Ca 2+ 0.2%, K + 14.0%, Mg 2+ 9.0%, Cl - 48.0%, SO4 2- 2.0%, with the remainder being water of crystallization and trace impurities. A mixed salt solution (potassium chloride, potassium sulfate, magnesium sulfate, and water in a mass ratio of 3.5:2.0:8.0:86.5) was added to carnallite, with a liquid-to-solid ratio of 3.2 mL:1 g. The mixture was stirred at 400 rpm for 1.8 h at 30 °C for salting-out crystallization. After the salting-out crystallization was completed, solid-liquid separation was performed to obtain crude potassium chloride solid and magnesium-containing decomposition mother liquor. The grade of crude potassium chloride solid reached 86.5%. (2) Add water to the magnesium-containing decomposition mother liquor obtained by separation as a mixed salt solution for the next salting-out crystallization transformation, and return to step (1) for recycling. The mass ratio of magnesium-containing decomposition mother liquor to water is 2.3:1. (3) The crude potassium chloride solid was rinsed twice in a countercurrent manner with a rinsing solution (potassium chloride, potassium nitrate and water in a mass ratio of 23:3:74). The liquid-solid ratio of the rinsing solution to the crude potassium chloride solid was 1.5 mL:1 g. The mother liquor and impurities attached to the surface were removed. After drying, the potassium chloride product was obtained with a grade of 93.8%. The rinsing solution was recycled for the next rinsing of the crude potassium chloride solid and was reused.

[0054] After seven cycles, the overall recovery rate of potassium chloride reached a stable level of 81.72%, with an overall grade of 93.27%.

[0055] The method of this invention is based on K + Mg 2+ / / Cl - The H2O system phase diagram utilizes the solubility difference between MgCl2 and KCl in a mixed salt solution (circulating mother liquor) at room temperature in carnallite. MgCl2 is highly soluble, while KCl has low solubility. By precisely controlling the amount and composition of the mixed salt solution (circulating mother liquor), MgCl2 selectively enters the liquid phase, and KCl recrystallizes out after supersaturation, then is washed with an eluent. The recrystallized mother liquor, after adding water, can be recycled as the mixed salt solution for the next extraction process; simultaneously, the eluent is also recycled until saturated. This invention achieves potassium-magnesium separation at room temperature without heating or evaporation, and the mother liquor can be recycled. It has advantages such as simple operation, low cost, short process, environmental friendliness, high potassium grade and recovery rate, and ease of industrialization, making it suitable for efficient potassium extraction from carnallite.

[0056] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for extracting potassium chloride from carnallite, characterized in that, It includes the following steps: 1) Carnallite is mixed with a mixed salt solution and then subjected to salting-out crystallization to obtain a reaction slurry; 2) The reaction slurry is subjected to solid-liquid separation to obtain crude potassium chloride solid and magnesium-containing decomposition mother liquor; 3) The crude potassium chloride solid was leached countercurrently with a circulating leaching solution. The leached solid was then dried to obtain potassium chloride.

2. The method for extracting potassium chloride from carnallite according to claim 1, characterized in that, Step 2) The magnesium-containing decomposition mother liquor is mixed with water and returned to Step 1) as a mixed salt solution for recycling. The mass ratio of magnesium-containing decomposition mother liquor to water is 1~4:

1. Step 3) The rinsing liquid generated after countercurrent rinsing is collected and not discharged externally. It is returned to Step 3) as the rinsing liquid for the next batch of crude potassium chloride solid. Steps 1) to 3) are repeated multiple times, with each cycle lasting 5 to 8 times.

3. The method for extracting potassium chloride from carnallite according to claim 1 or 2, characterized in that, The carnallite is an ore obtained by sun-drying in potassium-containing brine or salt pans; the carnallite contains the following components by mass fraction: Li + 0.1~0.6%, Na + 0.1~0.5%, Ca 2+ 0.05~0.25%, K + 12.2~14.5%, Mg 2+ 8.5~10.4%, Cl - 45~52%, SO4 2- 0.5%~5%.

4. The method for extracting potassium chloride from carnallite according to claim 3, characterized in that, The mixed salt solution is a circulating mother liquor, and the solvent of the mixed salt solution is water. The mixed salt contains one or more of potassium chloride, potassium sulfate, magnesium chloride, magnesium chloride hexahydrate, and magnesium sulfate.

5. The method for extracting potassium chloride from carnallite according to claim 4, characterized in that, The liquid-to-solid ratio of the mixed salt solution to carnallite is 1.5~4 mL:1 g.

6. The method for extracting potassium chloride from carnallite according to claim 5, characterized in that, The salting-out crystallization transformation is carried out at a temperature of 8~35℃ and a time of 0.5~2.5h under stirring conditions.

7. The method for extracting potassium chloride from carnallite according to claim 1 or 6, characterized in that, The rinsing solution is one or more of potassium chloride, potassium sulfate, potassium nitrate and water, and the number of countercurrent rinsing cycles is ≥1.

8. The method for extracting potassium chloride from carnallite according to claim 7, characterized in that, The liquid-to-solid ratio of the leaching solution to crude potassium chloride solid is 0.2~3 mL: 1 g.